1. Field of the Invention
This invention relates to poles, pilings, railroad cross-ties, and load-carrying structures, such as beams, columns and pallets made up of linear bamboo fibers bonded to, and surrounded by, synthetic polymers and to processes of preparing these structures.
2. Description of the Related Art
Presently, wood timber beams, columns and lumber depend on specie and dimensional size as the only engineering variables. Paint and other chemical treatments are used to lengthen the life of wood products that are exposed to the elements. However, there has been a growing concern over these toxic chemical treatments. Creosote, which has been used for years, is now considered to be a carcinogen, and has been banned from marine timber applications where immersion allows seepage into surrounding waters. Railroads are similarly concerned about creosote treated cross-ties. Utility companies are aware of the danger these preservatives present to their linemen and material handling people. Managed forests are producing faster growth but lower grade timber than was available a few years ago. This new timber sometimes does not pass the ANSI standards for timber pole structures.
Concrete with reinforcing steel has a greater ability to be custom engineered for various specific applications. However, the resulting products are extremely heavy, and in the case of load-carrying structures, such as bridges, the greatest portion of the structure is involved in holding itself up. This extreme weight forces many concrete structures to be fabricated on-site as opposed to being built in the factory. This adds greatly to the cost of these products. Also, concrete is very sensitive to motion, such as caused by earthquakes. Thermal expansion and freeze-thaw cycles wreak havoc on concrete components. A lightweight load-carrying beam, column or cross-tie that would not be sensitive to seismic or temperature changes would be a very desirable replacement for concrete.
Structural steel is extensively used for beam and column applications due to its strength, workability, and other factors. Steel has an on-going maintenance problem due to rust and corrosion that shortens its life span. Also, energy costs to produce steel and to fabricate and maintain steel components are quite expensive, keeping the price of the raw materials and finished products high.
Fiberglass is being researched and new products are being developed regularly, but the high cost of glass fibers and the resin matrices has proven to be a formidable barrier to overcome.
One particular application that has been traditionally filled by wood products is the construction of pallets. A typical wood pallet is approximately 40 inches by 48 inches by 5 inches and comprises a plurality of top slats and bottom slats supported on edge oriented 2xc3x974xe2x80x3 timbers. The market for such pallets is several million each year. While this market is a substantial drain on the timber industry, such wood pallets are not a preferred pallet for the food industry. In the food industry, contamination is a problem and efforts have been made to create a sanitizable pallet for re-use. Various efforts have been made to create a plastic pallet but such efforts have been largely unsuccessful for at least two reasons. A first reason is that plastic, as its name implies, will deform in response to load and therefore creates a failure condition when loaded pallets are mounted on edge racks in warehouse storage. A second problem is that plastic is substantially more expensive than wood raising pallet costs by several multiples. Accordingly, it would be advantageous to provide a structural substitute for wood and plastic in the pallet industry.
Bamboo has been considered for use in weight-bearing structures. Thus, Chemical Abstracts 107:135345q (1987) discloses composite materials containing 0.3-1 mm long bamboo strips, powdered bamboo, powdered wood, and resin in a molded piece. Chemical Abstracts 122:107321v (1995) discloses bamboo fibers as a reinforcing material for resinous composite structural panels. Chemical Abstracts 122:241192g (1995) discloses bamboo fibers and strips as reinforcing materials for thermosetting resin structural materials. Chemical Abstracts 118:148517z(1993) discloses strands of bamboo fibers as reinforcing materials for resinous laminates. Chemical Abstracts 117:173557z (1992) discloses bamboo fiber reinforced plastic structural materials. This reference also teaches a perfect bonding between the bamboo and the resin. Chemical Abstracts 116:199922u(1992) discloses bamboo fibers treated with a binding agent used in concrete structural materials. U.S. Pat. No. 4,774,121 to Vollenweider, II discloses blocks comprising stalks of bamboo surrounded by plastic foam cut into thin sections and coated with fiber reinforced plastic to be used in boat construction. The inventor has found that, contrary to the teachings of Chemical Abstracts 117:173557z, the use of untreated bamboo fibers as reinforcing agents for resinous structural materials results in slippage between the bamboo fibers and the resin matrix.
The present invention seeks to eliminate the above-noted disadvantages by providing a low-cost, high-strength composite formed from linear bamboo fibers bonded to synthetic polymers with binding agents which have been found to provide exceptional binding between the bamboo fibers and the polymer matrix. These composites can replace wood, concrete, steel, or fiberglass reinforced polymers in poles, pilings, and load-carrying structural applications such as pallets.
This invention seeks to provide an improved composite that has the ability to overcome the disadvantages of the presently available structural materials. In accordance with this invention, a composite structural piece is provided which comprises linear bamboo fibers bonded to and surrounded by synthetic polymers such as thermoplastic and thermosetting resins. In one form, the fibers are formed in elongated strips with an outer polymer coating and compression cut into short stubs which can be used in place of conventional plastic nodules in an injection molding machine. Products formed by injection molding using this form are lighter in weight and stronger than items molded of plastic alone.
In preparing the products of this invention, bamboo fibers of dimensionally equal sizes are treated or primed with a bonding material to be described below so as to accept a synthetic polymer. The fibers may take the form of split culms or tape. The products may be prepared by extruding a mixture of primed linear bamboo fibers and synthetic polymers or the product may be prepared by molding the mixture. The products may desirably take the form of beams, columns, poles, dimensional lumber or other structural products.